. >>> to politics now, president obama calls it one of the worst kept secrets in washington. had announced one of his closest aides will be his next chief of staff denis mcdonough succeeds jack lew. mr. obama says nobody outworks mcdonough. >> he's been one of my closest, most trusted advisers. he has been an indispensable member of my national security team, as well. denis has played a key role in every major national security decision of my presidency. >> he will be mr. obama's fifth chief of staff as the white house tackles the budget and immigration. >>> vice president biden says the country cannot remain silent after last month's school shooting. the vice president said the 2007 virginia tech massacre shows how important background checks are to keep guns out of the wrong hands. >>> president obama and secretary of state hillary clinton are parting ways. clinton is leaving her job at the state department next week. they sat down together for an interview with "60 minutes." and we'll have some of that for you in 30 minutes. >>> for much of the country this morning, it is